The invention relates to devices and methods for determining the availability of electrical energy, in particular in on-board electrical systems, on the basis of with a plurality of energy-storing means, in particular two of them, in motor vehicles.
Two-battery on-board electrical systems, or on-board electrical systems with two energy-storing means, are known for instance from German Patent DE-P 196 45 944. They typically serve to optimize the electrical energy supply in motor vehicles and have as their primary characteristic a second battery or energy-storing circuit, which depending on the operating state has an electrical coupling or decoupling with or from the main battery circuit. The main battery circuit, which is also called the consumer battery circuit, includes the usual consumer battery, the generator, and most of the electrical consumers. The connection between the first battery circuit (main battery circuit) and the second battery circuit is made via switch elements, which are triggered for instance by a control unit, in particular the so-called on-board electrical system control unit. The switch elements may also be components of the control unit.
The second battery circuit serves to supply consumers that primarily require the electrical supply for only a brief time. Such brief consumers are for instance high-current consumers, such as the starter or an electrically heatable
d. Electrical supply to consumers for a length of time Td, in particular for high-current consumers, or reinforcing supply to the first battery circuit.
For the chronological distribution of the modes of operation over the total service life of the vehicle, the following relationship can be assumed:Ta +Tb >>Tc >Td.
In known systems, the availability of stored energy in batteries is determined by means of complicated state of health/state of charge (SOH/SOC) algorithms and by means of a complicated system of current, voltage and temperature sensors. This can be achieved with an accuracy of only approximately ±5% to 10%. A disadvantage of the known method, besides the expenditure for the sensors and the requisite placement of these sensors in the immediate vicinity of the battery, is that monitoring the energy flow path between the battery and the consumer subsystem is generally additionally necessary, which requires increased availability of electrical energy.